Core Web Vitals is the name of the three core metrics Google uses to measure page experience. They measure how quickly a page appears, how fast it responds to clicks and how stable it stays while loading. In short, they put numbers on the things behind a visitor saying "this site is fast" or "this site is annoying."
In this article we walk through the three metrics one by one with everyday examples. We have also included how to measure your site and the most common problems.
The three metrics and Google's thresholds
For each metric, Google defines three zones: "good," "needs improvement" and "poor." The values below are the thresholds Google publishes in its web.dev and Search Console documentation.
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | Time until the main content appears | 2.5 seconds or less | Over 4 seconds |
| INP (Interaction to Next Paint) | Response time to a click | 200 milliseconds or less | Over 500 milliseconds |
| CLS (Cumulative Layout Shift) | How much the page shifts | 0.1 or less | Over 0.25 |
One important detail: Google does not assess these values by the average, but by the 75th percentile of visits. In other words, if three quarters of your visitors have a good experience, the page counts as "good."
LCP: when does the main content appear?
LCP is the time it takes for the largest image or text block on the page to render on screen. On corporate websites this is usually the big hero image or slider on the home page. For the visitor it means: "Has the page loaded, or am I still waiting?"
The things that hurt LCP most are large uncompressed images, slow server response, and too many plugins or font files that delay rendering. A common mistake is setting the main image to "lazy load"; the most important image on the page should load first.
INP: how long do you wait after a click?
INP replaced the older FID metric in March 2024. FID only looked at the delay of the first click; INP looks at clicks, taps and keyboard interactions throughout the visit and reports one of the slowest. If you tapped the menu and it opened half a second later, INP catches it.
The main cause of poor INP is the browser having to run too much JavaScript at once. Chat widgets, multiple tracking codes, heavy sliders and code added by page builders are typical sources.
CLS: why does the page jump around?
You click on a news story and start reading, then an ad appears at the top and the text slides down. Or a button moves just as you are about to press it. CLS measures the total of these shifts.
The fix is usually simple: reserve dimensions for images and ad slots in advance, place late-loading elements such as cookie notices so they do not push content around, and make sure fonts do not make text jump while loading.
How do you measure your site?
There are two kinds of measurement, and it is important not to mix them up:
- Field data: Data collected from real visitors' Chrome browsers. The Core Web Vitals report in Search Console and the top section of PageSpeed Insights show it. This is the data Google relies on for its assessment.
- Lab data: A simulation run on a single test device, shown in the lower section of PageSpeed Insights. It is useful for finding the cause of a problem but does not exactly reflect real experience.
On sites with little traffic, field data may not appear at all. In that case, lab results and a simple test on your phone will guide you. We cover the general reasons for a slow site separately in our article why is my website slow.
How much do Core Web Vitals affect rankings?
The honest answer: Google openly says page experience is considered by its ranking systems, but relevance of content is far more decisive. A slow but excellent page can outrank a fast but thin one. Still, speed makes a difference between pages of similar quality, and more importantly, a slow site loses visitors regardless of Google.
Practical checklist
- Test your home page and your two most visited pages for mobile in PageSpeed Insights.
- If the main image exceeds 200-300 KB, compress it and convert it to a modern format (WebP or AVIF).
- Remove unused plugins and old tracking codes.
- Make sure width and height are defined for images.
- Check the Core Web Vitals report in Search Console once a month.
How we do it at Globya
Speed problems rarely come from a single place; they get solved when the server, theme, plugins and content are handled together. That is why we do not separate our hosting and maintenance work from our SEO and GEO work. When building a new corporate website, we target the Core Web Vitals thresholds from the start and verify them with mobile measurements before launch.
Everything is green on desktop and red on mobile. Which one should I look at?
Look at mobile. Google evaluates sites primarily through their mobile version, and a large share of your visitors most likely comes from phones.
Does my PageSpeed score have to be 100?
No. That score is a summary of a lab test. The real goal is for all three metrics to be in the "good" zone in field data.
Can these thresholds be met on a site using a ready-made theme?
Often yes, but the load from the theme and plugins must be reduced. With some heavy page builders, lasting improvement may require restructuring the site.
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